Method of treating cellulosic fibrous materials



Patented Nov. 5, 1940 FIBROUS MATERIALS William Beach Pratt, Boston, Mass.; Annette Harris Pratt,1administratrix of said William 1 Beach Pratt,'deceased, assignor to Aldox Cor- -poration, Dover, Del., a corporationrof Delaware I v No Drawing, Application May 12, 1937, -SerialNo.142,32ll

4 Claims. (Cl. 8 116) My invention is a new cellulose hydrate resulting from the substitution of water for the aldehyde radical of aldehyde cellulose; and'a meth-'- od of making aldehyde cellulose and of substituting water for the aldehyde radical by the oxidation of the latter inthe presence of water.

By my invention there may be produced from cellulose fibres having waxes or gums combined therewith, acellulose hydrate product character- 10 ized by densened unshrunken and unswollen fibres which are markedly hygroscopic.

My invention is applicable to the treatment of cellulose in the form of fibres, filaments, yarns,

or fabrics, and when utilized in connection with cotton and bast fibre fabrics greatly improve the bleaching, sheen, hand, and dye-absorption and tinctorial effect. When applied to fabrics containing skein dyed yarns, my invention increases the fastness and brilliancy of the colors,

and woven fabrics treated in accordance with my invention suffer substantially no perceptible shrinkage even though no weftwise stretching is applied to the fabric during or after processing. In the application of my invention to products containing cellulose fibres having waxy or gummy constituents, such constituents preferably have their melting points lowered and their S01! ubility increased by the action ,of an aldehyde thereon in the presence of a detergent in an aqueous bath, and in the absence of any reagent tending to form condensation products with the aldehyde or having an afiinity for the aldehyde present, greater than the affinity of, the cellulose for such aldehyde. When the treatment 'is carried on under atmospheric pressure,,the temperature should be sufficiently high for .the ready emulsification with water of the softened waxes and gums and not sufliciently high to cause a wasteful loss of the aldehyde from-its aqueous 40 solution. However, the lossof aldehyde'from its aqueous solution at temperatures up to boiling may be retarded and in fact counteracted by running the fabric undergoing treatment across thev top of the bath, above thesurface thereof,'

and back into the bath so 'as toprovide aspecies of scrubbing action by which escaping aldehyde vapors are returned to and dissolved in the bath. The detergent used is preferably a neutral soap, and any tendency toward decomposition of such detergent with consequent formation of condensation products may be counteracted by the addition of borax to the bath. My process is preferably carriedon at a temperature well below the decomposition point of the detergent used and above the temperature at which waxy and gummy constituents'of 'the fibre'have their melting-point loweredby the action 'of the aldehyde airid'readilyenfulsify.For the treatment of cotton fabrics and-linen'fabrics I have found the most desirable range of temperatures to be 5 between F. and boiling. -Whileithe aldehyde acts on the gums and waxes and combines with the-cellulose slowly at temperatures'as low as IO4"F.,"I have found that-for the commercial treatment of cotton fabrics andlinen fabrics it 10 is desirable that the temperature should be between'160" F. and boiling, and that unless some provision is made for recapturing and returning to the bath the aldehyde gas escaping therefrom, it is preferable that the temperature of the bath 15 should not materially exceed -F. By the removal of the gums and-waxes fromthe fibres in a short period of time and at temperatures below theboiling point, the-original lustre value and physical properties characteris- 20 tic of naturalfibres are maintained to a degree which is impossible where'th'e fibres are subjected to high temperatures and long treatment in aqueous alkali solutions which have been heretofore considered necessary for-the removal 25 of such natural gums and-waxes. The action of the aldehyde appears todensen the fibres and cause a more uniform fibre surface which con-- tributes to the physical appearance and lustre of my treated fibre and which to a' degree follows 30 the factor of hydration. 1

But whether the characteristic lustre secured by my process is primarily due to the ultimate hydration of the fibre or to th'e'contraction or densifying of the, fibre by'the reaction of the 35 aldehyde, or to the avoidance of the deleterious effects of high temperatures or long aqueous alkali treatmentsyit is a fact that the fibres treated by the herein described process have lustre and hygroscopic qualities characteristic of 40 such treatment, and in effect similar to those produced by mercerizationbuthavephysical characteristics identifiably different. from the. physical characteristics resulting from mercerization. 1 I V r i 45 In determining the degree of hydration result ing from my process there are used the stand: ard methods for determining the degree of hydration resulting from mercerization. But exf amination' of the fibres show that no swelling has so taken place such as is always recognizable in by drated fibres resulting from mercerization, and my fibres retain the fiat ribbon-like characteristics of natural fibre which has never been treated in aqueous solution, although they may 55 be uncoiled or untwisted to some degree. These factors together render definitely recognizable fibres treated by my process even after they have been dyed or subjected to such forms of finishing as are commercially employed in the textile art. Moreover, goods treated in accordance with my invention have as soft hand" after bleaching with sodium hypochlorite as have goods bleached with hydrogen peroxide, thereby rendering more available and valuable the use of sodium hypochlorite as a bleach.

When yarn or piece goods treated in accordance with my invention are subjected to stretching, they show decreased plasticity and comparative uniformity in breaking strength whether wet or dry. This introduces markedly different factors of shrinkage in such yarn or piece goods and imparts valuable non-shrinkage characteristics which, however, vary through differences in construction as to twist of the yarn and weave of the fabric.

In the commercial practice of my invention, the efficient and economical removal of the ums and waxes, and subsequent hydration of the cellulose and its ultimate bleach are largely dependent on the proper carrying out of the steps requisite for the conversion of the natural cellulose into aldehyde cellulose.

To produce the effects hereinbefore described on the gums and waxes and convert the natural cellulose into aldehyde cellulose, I utilize an aqueous bath of formaldehyde gas in solution. I may form such baths by diluting with water standard commercial aqueous solutions of formaldehyde of say 37 to 40 concentration, or I may employ reversible polymerization products of formaldehyde free from extraneous substances, such as trioxymethylene or para-formaldehyde. Where commercial formaldehyde solutions are used, the gas diffuses uniformly through the bath regardless of the water temperature, but where paraformaldehyde or trioxymethylene is employed, the temperature must be raised to at least 160 F. to insure complete diffusion of the gas liberated from these polymerization products.

But even when a diluted commercial solution of formaldehyde is employed, the bath should be maintained at a temperature of at least 160 F. in order that the free formaldehyde gas presented in the solution may adequately act on the waxes and gums and react with thecellulose to form aldehyde cellulose.

The bath should be free from substances tending to react with the aldehyde such as are commonly used in kier boiling cellulose products, as for instance soda ash, vcaustiesoda, trisodium phosphate, or sodium bisulphiteand from such soaps as tend to break down readily and release alkali. The presence of such substances results in reaction therewith of the aldehyde to form insoluble condensation products which may stain the goods and prevents the liberation of free aldehyde gas and the formation of aldehyde cellulose; In fact, the addition of such substances to a bath containing free aldehyde gas and cellulose undergoing my treatment precludes the attachment of an aldehyde radical to the cellulose and effects removal of aldehyde radicals therefrom, due apparently to a selective affinity and reaction between the aldehyde and the alkali substances. The formation of objectionable condensation products from the reaction of the aldehyde with the alkali substances will take place at lower temperatures than the temperature atwhich alproducts from the injurious effects of alkalis in kier boiling, such condensation products are distinctly inimical to the practice of my invention, and preclude the successful formation of aldehyde cellulose if present in material quantity.

The reaction of the aldehyde on the gums and waxes inherent in the natural cellulose fibres appears to be both chemical and physical. Their melting points are lowered and they appear to change in surface tension to increase water adsorption. They are rendered byv my treatment readily removable from the cellulose by washing, particularly when proper detergents or emulsifying agents are employed.

By my invention there may be produced from cotton fibres or bast fibres a substantially pure cellulose fibre in a highly hydrated state without the objectionable swelling and shrinkage of fibres incident to mercerization and without any need for holding goods under tension during treatment. By hydrated I mean that there is formed a bond between the cellulose and a molecule of water which is not removable by a drying heat which removes all the freeor occluded water from ordinary cellulose or cellulose which has been rendered water absorbent by prolonged digestion in water.

While the presence of alkaline substances tending to react with aldehyde is deleterious, it is advantageous to add to the bath detergents, such as neutral soap and borax. The soap should, however, be tested to see that it will not break down or react with aldehyde in solution at the temperature and during the period requisit for the reaction of the aldehyde with the cellulose to form aldehyde cellulose, the addition of borax further insures against the baneful effects of such contingency, co-operates with the soap in facilitating the removal of the gums and waxes from the fibres and their emulsification in the aqueous solution, and lowers the pH of the solution.

The addition of soap is particularly desirable where trioxymethylene is used as the source of aldehyde. The soap and trioxymethylene may, be mixed in the dry form with or without the addition of borax in suitable proportions to provide for their introduction into the bath, in quantities based on the weight of the goods to be treated,-to secure the best possible wetting-up and penetration and the ultimate removal of the Waxes and gums by washing. When the chemical and/or physical reaction has taken place between the aldehyde and noncellulose constituents of the fibre, the soap and borax materially assist in reducing the time necessary for washing cotton sheeting is treated in of dry natural soap, 'such weight of borax. These ingredients are preferably mixed togetherin a mechanical mixer 2,220,804 to the amount of water and to the weight of the ment two percent (2%) of such weight of trioxymethylene, two percent (2%) of such weight and two percent (2%) of and dissolved in sufficient water to thoroughly saturate and completely immerse'the goods-and permit agitationof the goods therein. I

The treatmentpf the goods in the bath may take place in any form of suitable container,'I have found it convenient to carry on'the treatment in a standard form of dolly washer having a tank containing the bath in which the goods are piled or pleated, and from whichthey are drawn from and returned to the bath ,by a rotating reel, the goods preferably passing between squeeze =rollson their emergence from the bath.

'By the use of such washers, higher temperatures expedite the treatment withaldehyde gas, since the gas may be employed to out excessive loss of rising from the surface of the bath is'entrained in the wet goods passing over the reel and returned to the bath. When goods are being treated by batch operation,'they may be continuously circulated through the same bath until the elimination of gums and waxes and. the formation of aldehyde cellulose is completed and the aldehyde in the bath substantially exhausted. It is, however, generally preferable to carry on the treatment as a continuous operation bypassing the goods in a continuous strip through a series of washers in each of which a constant concentration of aldehyde and detergent may-be main,- tained by fortification of the bath froma source of concentrated solution and the addition of hot water as may be required.

Many other forms of washers, gigs, open tanks or even kiers having surfaces inert tothe reducing action of the bath, may be successfully used in giving the aldehyde treatment, as, for instance, the goods maybe fed through one or a series of ,J-boxes .having their lower portions immersed in aldehyde solution, the goods being fed to and folded in the upper part of the ,J-box and withdrawnfmm the lower endthereof and through squeeze rolls toeffect the treatment of the goods either in a batch operation or in a carry tinuous operation. The time required for treat! ment varies with the type of the goods and the temperature of the. bath. Forinstance, a treatment for an hour and a half will sumce where a temperature near boiling, whereas a three hour treatment may be required for the same fabric in an open tank at a temperature around 180 F. It'is desirable that the treatment be continued until substantially all the cellulose has been converted into aldehyde cellulose in which the aldehyde radical is so firmly attached as to be irremovable from the cellulose even by prolonged boiling in water. The time and temperature conditions under which this may be most economically efiected under any particular factory conditions and with specific types of goods may be empirically determined and the presence of aldehyde goods for an I it a fifteen minute t'eatmenton the water, bath radical v the aldehyde into'a water soluble acid in the a dolly washer at,

cellulose ascertained by test. A simple test is to thoroughly removeythe free gums and waxes from the aldehyde-treated goods by washing in hot water, then boiling a. sampleof the washed hour indistilled water, and giving at a temperature of over 180.! F. in Fehlings so 'lution. j" In making this test. there are employed (a) 69% aqueous solution of crystalline copper sulphate and (b) a mixture .of. 14% aqueous solution of sodium hydroxide and 34 aqueous.

solution of sodium potassium tartrate, Five per cent (5%) by volume of equal parts of Jo), and

(b) are mixed in thewater in which the samplejisflsubmerged, and at the endof the treatment,';there will'be uniform precipitation of oil:

prous oxide throughout the fibres convertedinto aldehyde cellulose.

When the cellulose of the/goods has been converted into'aldehyde cellulose as above described, the goods "are thoroughly'washed, as,. forin stance, in a rope wa'sherQfor the removal ofall' extraneous and non-cellulose material in preparation for the conversion of thealdehyde cellulose into fcellulose' hydrate by the substitution of water for the aldehyde radical. It is advisable in such washing to. use three changes of hot 'water, followed by 'a cold rinse. I

The ubstitution of water for the aldehyde is preferably'efiected by the oxidation of presence ofv water.

'The oxidation of, thealdehyde in the presence of water may beefflciently andv economically effected by the use. of a "solution, of sodium [hypochlorite, preferably of high chlorine content but of relatively lowalkalinity basedon the chlorine content. A sodium hypochlorite of i say -1 Twaddell is generallysatisfactory, 'whereas'if sodium hypochlorite. of relatively high alkalinity is used the'rate of hydration appears to be retarded and the removal of motes. and shives is less effective than when sodium hypochlorite of lower alkalinity is used. I J I The sodium hypochlorite'treatment maybe given in apparatus similar to that utilized for reaction between'the sodium hypochlorite and the aldehyderadicalsuch acid 's'houldbe removed from the goods during the reaction by passing the goods between squeeze rolls. r iOrdinarily' a treatment of th QOds for about thirty minutes in the hypochlorite solution at the usual temperature of factory practice of about 70 F. will suffice, during which time the goods should be passed aboutthreetimes through the squeeze-rolls and returned to the hypochlorite so andin the presence of this acid, hypochlorous" acid would-be produced. from the sodium hypochlorite, which would darken the goods and render it difficult to eifect a complete bleach thereafter. The treatment of the goods with an oxidizing agent for the removal of the aldehyde radical from the cellulose should not be confused with the use ofroxidizing agents to effect a usual bleach, for at the point in the treatment where the aldehyde treatment, and as acid is formed by aldehyde has been completely removed and cellulose hydrate hasbeen uniformly developed in the fibre the goods may show relatively little bleaching efiect, although they have been slightly lightcried in color. When the oxidation in the presence of water has effected the complete removal of the aldehyde radical and the hydration of the cellulose no precipitation of cuprous oxide in the fibres will result from a test with Fehlings solution, such as above described, to show the conmoved directly, without washing from" the '01:-

idizing and hydrating bath into a standard hypochlorite bleach, preferably of higher akalinity than the hypochlorite bath used for the oxidation of the aldehyde. The final bleach may be carried out continuously or in batches and in any standard manner to produce clear, white fabrics of good bottoming and a degree of hydration comparable to well mercerized goods. Where the fina bleach is unnecessary, the goods may be neutralized in the same apparatus in which the aldehyde was removed, thoroughly washed in cold water and finally given a hot wash. They are then ready for such use as may be desired Where a bleach is not required, and have the same degree of hydration as the bleached goods above described. Or the'neutralized washed grey goods so produced may be subjected to the action of types of bleaching agents, such as hydrogen peroxide or other standard bleaches. I

While I prefer to use aqueous sodium hypochlorite solution for the elimination of the aldehyde radical and the hydration of the cellulose, as well as. for the final bleach, other oxidizing agents may be used for converting the aldehyde into water soluble acid, as for instance, properly standardized dichromate, sodium or potassium permanganate or hydrogen peroxide. The use of sodium or potassium permanganate however involves the formation of products of reaction which must be removed before the final bleach. If hydrogen peroxide be used, the conversion of the aldehyde into an acid, in situ in the goods, progressively produces an acid reaction tending to retard the penetration of the active hydrogen peroxide through fibres and the removal of the aldehyde radical and complete hydration of the cellulose.

By my inventon I secure by a short and simple treatment at relatively low temperatures under atmospheric pressure as complete an elimination of non-cellulose constituents of cotton or bast fibres as is secured by the best'kier boiling for many hours with alkalies and at temperatures and pressures deleterious to the fibre and likely to cause oxidation by the presence of air in contact with the superheated yarn in the kier. By my invention I secure a degree of hydration, and dye absorption, comparable to the results of mercerization without the shrinkage and swelling of the fibres characteristic of mercerization, and the effects so secured on cotton and bast fibres produce new types of cellulose fibres capable of deflnite recognition.

This application is a continuation in part of myapplication Serial No. 31,443 on which Patent No. 2,126,809 issued August .16, 1933, after the deletion 01' all subject matter pertinent to the present invention.

Having described my invention, I claim: 1. In the treatment of natural cellulose fibre for the ultimate hydration thereof, the step which comprises subjecting the fibre to the action of formaldehyde solution devoid of substances having an affinity for formaldehyde greater than the affinity of formaldehyde for normal cellulose of the fibre at a temperature between 104 F. and boiling for a periodof time sufiicient to so combine formaldehyde with the cellulose of the fibre as to form a compound from which formaldehyde is irremovable by washing with water, the formaldehyde being in quantity sufficient to precipitate a visible deposit of copper on the cellulose of the fibre from a solution of copper salt.

2. The method of treating, as set forth in claim 1, cellulose fibre 7 containing natural gummy or waxy non-cellulose material until the meltin point of such material is lowered by the action of formaldehyde thereon.

3. In the treatment of natural organic fibres,

the step which comprises impregnating the fibres with formaldehyde in an aqueous bath having a temperature of the order of l60-180 F. and having formaldehyde volatilized therein from trioxymethylene and devoid of acid and substances free to combine or form condensation products with formaldehyde preferentially to the chemical combination of formaldehyde with such fibres.

4. In the treatment of natural cellulose fibres, the steps which include treating natural cellulose fibres having a waxy or gummy' constituent in an aqueous bath containing trioxymethylene and devoid of any substances free to combine or form condensation products with formaldehyde preferentially to the chemical combination of formaldehyde with cellulose and at a temperature above that at which formaldehyde gas is liberated from the trioxymethylene but below boiling, and until formaldehyde is so combined with the cellulose as to be irremovable by washing, washing out said constituent, and treating the cellulose combined with aldehyde with an oxidizing agent in the presence of water until the aldehyde component is converted into formic acid and removed and the cellulose is converted into cellulose hydrate without decomposition of the 

